Electrodes are used on a commercial scale in various electrochemical processes such as electrolyses, electrolytic treatments, and galvanic cells. Electrodes of various types and modes for various applications have been manufactured. These electrodes are preponderantly in the form of insoluble solids. Generally, metals or metal compounds such as oxides thereof which possess the activity and durability expected of any electrode are used either in the form of particles or deposited in the form of coatings on suitable substrates.
Insoluble electrodes formed by coating a substrate of metallic titanium with metal oxides including platinum group metal oxides, for example, are widely used on a commercial scale for electrolysis of aqueous solutions such as of sodium chloride. Electrodes formed of particles of metals or metal oxides and electrodes formed by sintering such particles or molding such particles with suitable binders have been used in electrolyses, electrolytic treatments, and galvanic cells.
Electrodes of the types described above can be prepared by various methods. Among these methods, the so-called thermal decomposition method which comprises the steps of preparing a liquid composition containing an electrode component metal and subjecting this liquid composition directly, or applied on a substrate, to a thermal treatment thereby converting the component metal into an electrode substance in the form of a metal or a metal oxide finds general acceptance as highly effective means.
Generally in this particular method, a composition containing a salt of a thermally decomposable electrode component metal and a solvent is subjected to a thermal treatment at an elevated temperature of about 250.degree. to 800.degree. C. Thermally decomposable salts which can be used include chlorides, oxychlorides, alkoxy halides, resinates, amines, etc. of various electrode component metals. As solvents therefor, water, hydrochloric acid, various alcohols, toluene, and benzene have been suitably adopted (as disclosed in Japanese Patent Publication No. SHO-48(1973)-3954 corresponding to U.S. Pat. No. 3,711,385 and Japanese Patent Application Laid-Open No. SHO 51(1976)-131475, for example).
When the conventional composition for electrode production is subjected to a thermal treatment aimed at removing the solvent through volatilization and thermally decomposing the salt of an electrode component metal into a corresponding metal, or further converting the metal into a corresponding metal oxide, however, the electrode component metal is often diffused in a large volume as volatilized in the form of a chloride in conjunction with the solvent results in serious problems including lowered product yield, impaired product quality stability, and inevitable environmental pollution.
As a measure, it has been proposed, where Sn is used as an electrode-coating component, for example, to use a sulfate of Sn instead of a chloride of Sn (as disclosed in Japanese Patent Application Laid-Open No. SHO 52(1977)-141489, for example). This method is effective in lowering the loss of the Sn component by volatilization to a fair extent but it is not sufficient at the present. Further, the danger due to use of sulfuric acid, a strong acid, is involved. With respect to the electrode components other than Sn, the aforementioned problems remain yet to be solved. Thus, it has been difficult to produce electrodes of various electrode components in a stable manner and in high yields by the thermal decomposition method.